The Magellanic Stream trails 180 degrees across the sky behind the Magellanic Clouds, two dwarf galaxies that orbit the Milky Way.

It is thought to be the result of gas being ripped out of the Magellanic Clouds by our larger galaxy.

The researchers used the Australia Telescope Compact Array near Narrabri, New South Wales, to detect the absorption of radio waves by hydrogen gas in the Stream.

Birthplace of stars?

Finding cold hydrogen in the Stream is significant as it is thought that cold gas is needed for stars to form.

Cold atoms move slower than hot atoms, and, in the presence of dust, eventually clump together to form molecular clouds, the precursor of stars.

The presence of cold gas may indicate that the Stream is a type of stellar birthplace previously unknown in astronomy.

But the researchers found no sign of the dust needed to form stars, despite also searching for the radio absorption signals of carbon monoxide, a common ingredient in star dust.

"Currently, the Stream isn't dense enough, and there's not enough dust to form stars," says Matthews.

If there are no stars forming, then it's unlikely the Stream could be the birthplace of new dwarf galaxies, she says.

"It's more likely the stream will [ultimately] fall onto the Milky Way galaxy."

Too early to tell

Astrophysicist Dr Geraint Lewis of the University of Sydney says the research is a "good clue" as to what happens to gas within the Stream, but believes the lack of dust does not rule out the possibility that stars and galaxies will eventually form.

"The big question is what's going to happen now," says Lewis. "To me it would suggest that the Stream is relatively young, so perhaps some gas has cooled, but not enough to form stars."

"They might just have caught this gas in a snapshot of its evolution as it is on its way to form stars."

Lewis says the find is "essentially keyhole surgery", and a bigger survey is needed before the ultimate fate of the Stream can be known.

"What we've got to get is a survey of a large part [of the Stream] to get a big picture of what's going on," he says.